Hi,
Thats one serious short youve got there! and should be easy to find due to the severity of it.
Say you got a 10aHr battery, it will supply 10amps for 1 Hr and 1amp for 10 Hrs, so in 20 mins will be losing 3amps- must be a near dead short!!. Using a multimeter set to high amps and with the bike off you would disconnect the batry negative lead and put the negative lead on the negative bat post. Put the positive lead to the negative earth lead you took from the bat and then come down the amp scale until you get a reading ( no reading=no short). Now remove and then repace a fuse at a time untill the short stops and this will show the circuit that has the short. You can then start to test this circuit e.g lights to find the short. If you find no short it could be reg/rec but seing as youve changed this id say its in the loom.